Minn. Stat. § 128D.17: INVESTMENTS.

The school board may invest any funds not currently needed by the district in bonds of the state of Minnesota, or in bonds of any county, city, home rule charter or statutory city, or school district in Minnesota, or in bonds of the United States, or in United States Treasury bills, certificates of indebtedness, or Treasury notes, all of which must mature within one year from the date of purchase.